As a synthetic route for a 2,2-difluoropropane, a method has been known which comprises adding dichlorodifluoromethane or trichlorofluoromethane to an ethylene having a difluoromethylene unit, such as 1,1-dichloro-2,2-difluoroethylene or 1-chloro-1,2,2trifluoroethylene, in the presence of aluminum chloride.
However, such a method has a drawback that it produces not only the desired product but also a reaction by-product having a methylene group other than the 2,2-difluoromethylene and having a boiling point close to that of the desired product, whereby a multi stage purification process is required in order to obtain a product of a high purity. Further, a method for synthesizing 1-chloro-1,1,2,2-tetrafluoropropane is known which comprises fluorinating propyne (CH.sub.3 C.tbd.CH) with hydrogen fluoride to obtain 2,2-difluoropropane (CH.sub.3 CF.sub.2 CH.sub.3), then selectively chlorinating only three hydrogen atoms at 1-position with chlorine to obtain 1,1,1-trichloro-2,2-difluoropropane (CCl.sub.3 CF.sub.2 CH.sub.3), and further selectively fluorinating only two out of the three chlorine atoms substituted on the carbon atom at the 1-position to obtain 1-chloro-1,1,2,2-tetrafluoropropane (J. Am. Chem. Soc., 65, 2342 (1943)). This method requires many steps and thus has a drawback that it is difficult to improve the yield, and the method is not suitable for industrial production. Further, a method for preparing 1-chloro-2,2,3,3-tetrafluoropropane is known which comprises producing 2,2,3,3-tetrafluoropropanol from tetrafluoroethylene and methanol, then reacting it with sulfuryl chloride to obtain a chlorosulfonic acid ester, and then reacting it with an alkali metal chloride. This method requires many steps, whereby it is difficult to improve the yield, and thus has a drawback that such a method is not suitable for industrial production.
Further, a method for preparing 1-chloro-2,2,3-trifluoropropane is known which comprises dehydrochlorinating 1,2,3-trichloropropane to obtain 2,3-dichloropropene, reacting it with potassium fluoride to obtain 2-chloro-3-fluoropropene, then adding chlorine thereto to obtain 1,2,2-trichloro-3-fluoropropane, and then fluorinating it with antimony dichloride trifluoride. Such a method requires many steps. Therefore, the method has a drawback that it is difficult to improve the yield. As such, the method is not suitable for industrial production.